As the screen generally isn't big enough for all your programs, most people have
multiple 'workspaces'. For example, you might put your web browser on one
workspace, a report you are writing on another, and so on.
The pager applet runs inside the ROX-Filer panel, and shows you a bird's-eye
view of all your workspaces. You can click on a workspace to navigate to it,
drag windows between workspaces, and get a menu of windows to bring one to the
front.
You will need a window manager that supports multiple workspaces; almost all of
them do (including OroboROX).